| Hydrophobically associating polymers have superior properties to partially hydrolyzed polyacrylamides,therefore,it shows great potential for application in chemical flooding.Its performance is not only related to the molecular structure(hydrophobic monomer content,molecular weight,degree of hydrolysis,etc.),but also closely related to the matching of the hydrodynamic size and reservoir.In this paper,through the seepage(homogeneous)and flooding experiments(homogeneous and heterogeneous)of similar shear viscosity polymer systems under different conditions,the inductive conductivity,oil displacement performance,and the establishment of seepage resistance of the associative polymers with different hydrophobic groups content were studied.The main content and conclusions are as follows:(1)Through the hydrolysis of aqueous solution after radical polymerization,different associative polymers were synthesized by changing the content of hydrophobic monomers.It has good solubility,similar molecular weight and similar degree of hydrolysis.Combining the critical association concentration and the displacement test requirements,the paper has determined the approximate shear viscosity(around 60mPa·s)polymer system at 20s-1.Rheological experiments showed that DM-2 had the largest degree of pseudoplasticity and the strongest thickening property,and the viscoelasticity was DM-2>DM-3>DM-1>DM-0.Steady-state fluorescence spectroscopy measurements show that the association strength increases first and then decreases with the increase of the hydrophobic monomer content,and the association density increases.The main reason for the higher viscoelasticity of DM-2 than DM-3 is that the contribution of the associative density of DM-3 is less than the contribution of the degree of association of DM-2.(2)The seepage characteristics of DM series polymers were studied in the range of 0.55-6.93?m2.The results showed that the polymers all showed good injection conductivity,but as the hydrophobic monomer content increased or the permeability decreased,the injection pressure increased,the time from the beginning of the pressure rise to equilibrium increased,and the pressure difference in each segment increased.At the same time,the associative polymers(DM-1?DM-3)above and below a certain critical permeability exhibit two modes:Equal flow resistance&Increased flow resistance.DM-0 is always in equal flow resistance range.As the permeability decreases,the hydrophobically associating polymer is more likely to behave as increased flow resistance.As the hydrophobic monomer content increases,the critical permeability is higher,and the critical permeability is DM-1(1.88 ?m2),DM-2(5.03 ?m2),and DM-3(6.93 ?m2),respectively.Microfiltration membrane filtration and in situ detection of percolation effluent showed that the main mechanism of increased flow resistance is not adsorption,but the increase of aggregate size and increase of viscosity during percolation.(3)The homogeneity model was used to study the flooding characteristics of DM series polymers with similar shear viscosity under different permeabilities.Compared with DM-0,the associative polymer fingering phenomenon is weaker,especially when the hydrophobic monomer content is high,it shows piston displacement effect.When the injection volume is the same,the spread of DM-0 is good,but under the same affected area,the recovery factor of DM-0 is about eight percent lower than that of DM-2,indicating that the ability to increase oil recovery depends not only on the sweeping ability but also on the micro-displacement efficiency.Although DM-3 can establish higher seepage resistance than DM-2,the final recovery is worse than DM-2,indicating that the final recovery under homogeneous conditions corresponds to the optimal hydrophobic monomer content.In the range of equal flow resistance,elasticity plays a dominant role in flooding.The recovery of increased flow resistance is related to the amount of injection.In the initial stage,the molecular hydrodynamic size is the main factor,while the ultimate recovery is related to the viscoelasticity of the polymer,the size of the molecular hydrodynamics,and the pore throat size.(4)Experiments in heterogeneous models with different permeability contrasts shows that under all permeability contrast increase+increase has the highest ultimate recovery.The polymer with higher hydrophobic monomer content preferentially enters the low-permeability zone under the high permeability contrast.There is a matching relationship between the hydrophobic monomer content and the permeability contrasts,and the higher the hydrophobic monomer content,the more suitable the high permeability contrast.The best matching relationship in heterogeneity is independent of injection volume.Associative polymers with different hydrophobic monomer content have adaptability and selectivity to reservoir permeability and permeability contrast.Under certain permeability conditions,the molecular hydrodynamic size does not affect the injectivity,In addition,use its good properties to enhance oil recovery.Under a certain permeability contrast,the seepage resistance established in the high-permeability zone and the low-permeability zone can just make the polymer alternately flow between them,improve displacing fluid distribution,establish reasonable suction hydraulic pressure to enhance ultimate recovery.The conclusion helps the hydrophobic associative polymer to play a positive role for reservoir conditions and reduce negative impacts.The dissertation can provide theoretical basis and guidance for designing and selecting appropriate associative polymers or selecting suitable reservoirs for associative polymers of specific molecular structures.It also can provide theoretical support for broadening use conditions,improving the design and performance of molecular structures,and enriching the mechanism of displacement. |
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